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Nobody has cracked GCHQ's crypto Christmas Puzzle

Spies like to think they're smarter than most people -- and they may just be right. More than 600,000 people have tried to complete GCHQ's Christmas puzzle but nobody has got it right, yet.

The grid-shading nonogram puzzle was set by GCHQ as part of its Christmas card, but was then made available to all online. (A high-res version can be found here). The initial puzzle is relatively simple to solve, but it leads to a further range of problems that are proving very tricky.

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In fact, GCHQ reports, no-one who has entered the challenge has been able to fully solve it. GCHQ said around 30,000 people have reached the final stage of the puzzle but it doesn't know whether anyone will be able to complete it before the deadline at the end of January. Not even the hivemind of Reddit has been able to crack the case.

To complete the first stage the grid must be filled out -- when finished, a QR code is given. The QR code leads to the next stage of the puzzle. In December Redditors and Guardian readers between them made it through to a third puzzle, which was based on a cryptic word search clues and on to a fourth number-sequence puzzle.

Since then Redditors have moved onto a fifth puzzle, which appears to have 12 different parts including algebra, a cipher and graph theory.

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Robert Hannigan the director of GCHQ, who apparently has plenty of time to be setting puzzles and competitions gave a clue to those who are trying to solve the problem. He said "It's not as abstract as you think". Those who take the puzzle on have also been encouraged to donate to NSPCC.

Previous puzzles from GCHQ have included everything from a hidden code in the snooping agency's website to cryptographic substitution ciphers.

The deadline for solving the puzzle is 23:59 on January 31 – and the only way to know how to submit your winning answer is to crack its final code...